 Thermogenic drugs, like DMP, can cause people to overheat to death, can increase resting metabolic rates by 300% or more. More physiological spread would range about 10 times less, from a 30% slower metabolism of people with an underactive thyroid to a 30% higher metabolism when the part of our nervous system that controls our fight-or-flight response is activated. In response to a fright or acute stress, special nerves release a chemical called noradrenaline to ready us for confrontation. You experience that by your skin getting paler, cold, and clammy as blood is diverted to your more vital organs, your mouth can get dry as your digestive system is put on hold, your heart starts to beat faster. What you don't feel is the extra fat being burned to liberate energy for the fight. That's why people started taking ephedra for weight loss. Ephedra is an evergreen shrub used for thousands of years in China to treat asthma, because it causes the same release of noradrenaline that offers relief to asthmatics by dilating their airways. In the United States, it was appropriated for use as a metabolic stimulant shown to result in about two pounds of weight loss a month in 19 placebo-controlled trials. By the late 1990s, millions of Americans were taking it. The problem is that it had all the other noradrenaline effects like increasing heart rate and blood pressure, and so chronic use resulted in strokes, heart arrhythmias, and death. The FDA warned the public of the risks in 1994, but it wasn't banned until a decade later after a major league pitcher dropped dead. In the current wild west of dietary supplement recommendation, a supplement can be marketed without any safety data at all, and the manufacturer is under no obligation to disclose adverse effects that may arise. No surprise, then, that online vendors assured absolute safety, no negative side effects, 100% safe for long-term use. The president of Metabolife International, leading seller of ephedra, assured the FDA that it the company had never received a single notice from a consumer that any serious adverse health event had occurred. In reality, they received 13,000 health complaints, including reports of serious injuries, hospitalizations, and deaths. If only there was a way to get the benefits of ephedra without the risks. There is, but to understand it, you first have to grasp a remarkable biological phenomenon known as the diving reflex. Imagine yourself walking across a frozen lake and suddenly falling through the ice, plunging into the icy depths. I'm starting to think about greater instant fight or flight shock than that. Indeed, noradrenaline would be released causing the blood vessels and your arms and legs to constrict to bring blood back to your core. You can imagine how fast your heart might start racing, but that would actually be counterproductive, right? Because you'd use up your oxygen faster. Remarkably, what happens instead is your heart rate actually slows down. That's the diving reflex. First described in the 1700s, air-breathing animals are born with this automatic safety feature to help keep us from drowning. In medicine, we can exploit this physiological quirk with what's called a cold-face test. To see if a comatose patient has intact neural pathways, you can apply cold compresses to their face to see if their heart immediately starts slowing down. Or more dramatically, it can be used to treat people who flip into an abnormally rapid heart rate. Remember that episode of ER where Carter dunks the guy's face into a tray of ice water? It was on TV when I was in medical school and a group of us would gather around and count how many times they violated universal precautions. OK, but what does this have to do with weight loss? The problem with noradrenaline-releasing drugs like ephedra is the accompanying rise in heart rate and blood pressure. But what the diving reflex shows is that it's possible to experience selective noradrenaline effects racing the possibility that there may be a way to get the metabolic boost without risking stroking out. Unbelievably, this intricate physiological feat may be accomplished by the most simplest of acts. Instead of a drowning in water, simply drinking it. Wait, what? You can boost your metabolism drinking water? Buckle your safety belts. You are in for a wild ride, which will continue next. This is the end of this episode. Thank you for watching. I hope you enjoyed it. I'll see you in the next episode.